The objective of this work is to study in mice the molecular basis of teratomas that arise from the germ cells. One aspect of the investigation requires that knowledge of the mechanisms of X chromosome inactivation be acquired since inactivation of the X chromosome seems to be a fundamental step in differentiation and possibly the development of teratomas. Our approach to this problem is to assess whether differences in the amount of an enzyme, phosphoglycerate kinase, which is coded for by a gene on the X chromosome, can be detected in primordial germ cells from female, male and X/O embryos. Another aspect of the problem is that since phosphoglycerate kinase, coded for by an X-linked gene, seems to be regulated coordinately with phosphoglycerate mutase and triosephosphate isomerase, two enzymes that are probably coded for by genes on autosomal chromosomes, information on the interrelations between genes on the X chromosome and those on autosome can be obtained by investigation of the basis of this coordinated regulation. The initial approach to this problem will be to produce specific antibody against the purified enzymes and determine their relative rates of synthesis and degradation.